The present invention relates to a method and apparatus for the impregnation of structural shapes formed by filament windings with thermoplastic binder.
Reinforced plastics are composite materials made up of fibers and polymeric binders that serve as matrices. Intricate shapes are possible with reinforced plastics, which are low density materials having high strength to weight ratios. Reinforced plastics enhance the desirable characteristics of low heat and low electrical conductivity of polymers and selected polymer resistance to water, acid, bass and solvents.
Thermoset resins are typically used in making reinforced plastics. For glass reinforced plastics, the reinforcement material and activated resin are placed in a spinning mold. The mold is heated to cure the resin and centrifugal force assures smooth inner and outer surfaces and the absence of voids in the composite material. This approach is not easily facilitated where the binder is a high molecular weight thermoplastic resin.
Another approach when thermoset resins are used as the binder in filament wound structures is to solution impregnate the fiber tows and then wind them onto a form. This approach is also not easily facilitated where the binder is a high molecular weight thermoplastic resin. Sufficient resin loading of the tow, the necessary amount of drape, and wet-out of the tow may not be achievable without a large number of unit operations.
Although most filament wound structures use thermoset binders, several approaches using thermoplastic binder impregnation have been described. In U.S. Pat. No. 4,319,944, the process involves helically winding strips of reinforced fabric and hot thermoplastic polymer onto a heated mandrel and passing the mandrel under a smooth roller to embed the fabric into the thermoplastic.
In U.S. Pat. No. 4,282,905, a reinforced circular tube is formed by placing a tube of thermoplastic within a close-fitting seamless fabric sleeve of an inert fiber, heating the tube to soften the plastic and expanding the softened tube by inflation or centrifugal force thereby forcing the polymer into the interstices of the fabric sleeve, and cooling the tubes so that an integral pipe is formed.
In United Kingdom Patent No. 2040786A a filament winding on a vertical mandrel is inserted into a mold containing the matrix resin. Impregnation is achieved by vibrating the mandrel or the mold.
In United Kingdom Patent No. 2105247A, thermoplastic yarn is wrapped around reinforcing fibers and the assembly heated under pressure to thermoform the wrapping yarn into a polymer matrix which incorporates the reinforcing fibers.
It is an object of the present invention to provide a method and apparatus for impregnating filament-wound structural shapes with a binder of thermoplastic resin.
It is a further object of the present invention to provide a method and apparatus for manufacturing continuous fiber composites with high molecular weight thermoplastics achieving uniform resin loading and little or no void space.